Cisco,CCNA,CCNP,Certification, computer Cisco CCNA / CCNP Certification Exam Tutorial: Dialer Watch
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Dialer Watch is a vital part of your CCNA and CCNP studies, particularly for the BCRAN exam, but it's one of the most misunderstood technologies as well. To help you pass the CCNA and CCNP certification exams, here's a detailed look at Dialer Watch.Dialer Watch allows you to configure a route or routes as "watched" when the watched route leaves the routing table and there is no other valid route to that specific destination, the ISDN link will come up. In the following example, R1 and R2 are connected by both a Frame Relay cloud over the 172.12.123.0 /24 network and an ISDN cloud using the 172.12.12.0 /24 network. The routers are running OSPF over the Frame cloud, and R1 is advertising its loopback of 1.1.1.1/32 as well as an Ethernet segment, 10.1.1.0/24, via OSPF. R2 has both of these routes in its OSPF table, as shown below.R2#show ip route ospf1.0.0.0/32 is subnetted, 1 subnetsO 1.1.1.1 [110/65] via 172.12.123.1, 00:00:07, Serial010.0.0.0/24 is subnetted, 1 subnetsO 10.1.1.0 [110/128] via 172.12.123.1, 00:00:08, Serial0We want R2 to place a call to R1 if either the loopback or Ethernet networks leave R2's routing table, but we don't want to have to depend on interesting traffic. That dictates the use of Dialer Watch. First, configure the list of watched routes with dialer watch-list. Only one of the watched routes needs to leave the routing table for the ISDN link to come up. In this example, R2 will watch both routes from its OSPF routing table.Be careful with this command. The entries here need to match exactly the routes and masks being watched. Dialer watch-lists use subnet masks, not wildcard masks.R2(config)#dialer watch-list 5 ip 10.1.1.0 255.255.255.0R2(config)#dialer watch-list 5 ip 1.1.1.1 255.255.255.255Configure the dialer watch-group command on the BRI interface, AND frame map statements for the watched routes. As with dialer-list and dialer-group, the group number referenced in the dialer watch-group command must match the number assigned to the dialer watch-list.The Dialer Watch configuration will not work without frame map statements for each watched route. I repeat this because this is the step a lot of people leave out.R2(config)#interface bri0R2(config-if)#dialer watch-group 5R2(config-if)# dialer map ip 1.1.1.1 255.255.255.255. name R1 5557777 broadcastR2(config-if)# dialer map ip 10.1.1.0 255.255.255.0 name R1 5557777 broadcastTo test Dialer Watch, the Serial0 interface on R2 will be shut down. Since we're running OSPF, the route table will be updated almost immediately and the ISDN link should come up right after that.R2(config)#int s0R2(config-if)#shut01:12:47: %OSPF-5-ADJCHG: Process 1, Nbr 1.1.1.1 on Serial0 from FULL to DOWN, Neighbor Down: Interface down or detached01:12:47: %LINK-3-UPDOWN: Interface BRI0:1, changed state to up01:12:48: %SYS-5-CONFIG_I: Configured from console by console01:12:48: %LINEPROTO-5-UPDOWN: Line protocol on Interface BRI0:1, changed stateto up01:12:49: %LINK-5-CHANGED: Interface Serial0, changed state to administrativelydown01:12:50: %LINEPROTO-5-UPDOWN: Line protocol on Interface Serial0, changed stateto down01:12:53: %ISDN-6-CONNECT: Interface BRI0:1 is now connected to 5557777 R1Within five seconds, the ISDN link is up. show dialer verifies that Dialer Watch is the reason the line was brought up.R2#show dialerBRI0 - dialer type = ISDNDial String Successes Failures Last DNIS Last status5557777 2 0 00:00:11 successful0 incoming call(s) have been screened.0 incoming call(s) rejected for callback.BRI0:1 - dialer type = ISDNIdle timer (120 secs), Fast idle timer (20 secs)Wait for carrier (30 secs), Re-enable (15 secs)Dialer state is data link layer upDial reason: Dialing on watched route lossTime until disconnect 108 secsConnected to 5557777 (R1)A final note regarding Dialer Watch ... it will not work with RIP, but will with all our other dynamic IGPs (IGRP, EIGRP, OSPF). Article Tags: Ccnp Certification, Dialer Watch, Watched Route, Routing Table, Isdn Link, Watched Routes, Interface Bri0:1
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